Plasma torch with axial supply of the stabilizing gas

ABSTRACT

A plasma torch with an internal cathode and an external anode coaxial of and surrounding the cathode, the anode forming a part of a plasma nozzle. The cathode and the anode have confronting similarly disposed frustoconical portions presenting a gap therebetween, the larger-diametered end of the cathode having a diameter generally the same as the smaller diametered end of the anode, whereby axial adjustment of the cathode and anode relative to each other adjusts the effective length of the gap therebetween. Means is provided to provide an axial flow of stabilizing gas between the cathode and anode, such means including means to adjust the stream of gas so as to comply with different operating conditions when the effective length of the gap between the cathode and the anode is changed. The construction is such that the cathode may be brought into contact with the anode to form a temporary short circuit there between for starting the arc discharge.

[451 Dec. 31, 1974 Primary Examiner-Herman Karl Saalbach AssistantExaminer-Darwin R. Hostetter Attorney, Agent, or Firm--Arthur O. KleinVladimir Dembovsky, Ostrava, Czechoslovakia F O m P P U S L m X A S A GG HN H R] m m A Mm m S n AE 6 Ln m PTI H 5 5 H.

[57] ABSTRACT A plasma torch with an internal cathode and an exter- [73]Assignee: Vysoka skola banska Ostrava,

Ostrava Czechoslovakia nal anode coaxial of and surrounding the cathode,the Feb. 6, 1973 anode forming a part of a plasma nozzle. The cathodeand the anode have confrontin frustoconical portions presenting [22]Filed:

g similarly disposed Appl. No.: 330,026

a gap therebetween, the larger-diametered end of the cathode having adi- [30] Foreign Application Priority Data ameter generally the same asthe smaller diametered end of the anode, whereby axial adjustment of theV cathode and anode relative to each other adjusts the Feb. 9, 1972Czechoslovakia 806-72 wm mm ms u a m egcma M zmm e m S n mw m effectivelength of the gap therebetween.

provided to provide an axial flow of stabilizin tween the cathode andanode, such means means to adjust the stream of different operatingconditio length of the gap between the cathode and the anode 5References Cited is changed. The construction is such that the cathodeUNITED STATES PATENTS may be brought into contact with the anode to forma temporary short circuit there between for startin arc discharge.

g the 3,130,292 4/1964 Gage et 3l3/DIG 6 3,242,305 3/1966 Kane et al3l3/DIG. 6

2 Claims. 3 Drawing Figures PAIENTED DECB 1 um SHEET 10F 2 v .IIII'I Illllll e l-iili PLASMA TORCH WITH AXIAL SUPPLY OF THE STABILIZING GASBACKGROUND OF THE INVENTION The invention relates to a plasma torch withare discharge and axial supply of the stabilizing gas solving theadjustment of the supply of the stabilizing gas, the adjustment of thedistance of the cathode from the anode with a possibility of starting byshort circuiting the cathode and anode and with a direct and intensivecooling of the nozzle.

Known plasma torches have either an axial or tangential supply of thestabilizing gas. The supply means of the stabilizing gas are generallystable and are suitable for certain operating conditions of the plasmatorch .Within a relatively narrow range of speeds of the gaseous mediumin the discharge chambers. The selection of the distance of the cathodefrom the anode has been for known plasma torches determined withoutregard to the circumstance that by changes of this distance, changes ofthe flow of the gas along the cathode are resulting, reducing theefficiency of burning of the torch. The electric are discharge is foractually known plasma burners started either by a purposely made shortcircuit between the cathode and anode either directly or by means of awire of a metal with low melting point or by means of an auxiliarydischarge between an auxiliary cathode and the anode of the plasmatorch. The electric arc discharge can be also started by means of a highfrequency or high voltage current causing a high frequency or highvoltage discharge in the discharge chamber, which causes ionization ofthe operating space and enables starting of the electric arc dischargeby the electric current supplied by the DC or AC main supply source. Themethods applying for the generation of a short circuit a wire of a metalwith low melting point have the drawback, that the low melting metalcontaminates not only the plasma torch, but also the plasma and in manycases also the molten material, so that this starting method cannot beused where a high purity of plasma is required. The application of anauxiliary electric discharge between an auxiliary cathode and the anodebrings about difficulties in design. The starting of the electric are byhigh frequency or high voltage current increases substantially the costof the whole arrangement.

The stabilizing gas is supplied to the nozzle at known plasma torchesvia an annular space, between the external cylindrical surface of thecathode and the internal surface of the nozzle. This arrangement of thegas supply however does not solve a uniform passage of the gas along thecathode, a sufficient cooling of its surface by the working gas andequally does not solve a centric discharge of the plasma from nozzleswith a larger diameter; The flow of the cooling liquid uses to bearranged for dirrectly cooled nozzles by means of channels, supplyingthe cooling liquid which comes in contact with a part of the nozzle onlyor free spaces around the nozzle are formed through which the cool-SUMMARY OF THE INVENTION It is an object of this invention to eliminatethe drawbacks of existing plasma torches and to enable an easyadjustment of the torch to different working conditions at an efficientcooling of the nozzle with an easy starting of the arc discharge.

The torch according to this invention has an axial supply of astabilizing gas, a cathode displaceable in the axial direction and anozzle cooled by a through flowing cooling medium, the cathode having onits surface longitudinal grooves, a distributing insert being providedbetween the external mantle of the torch and an internal tube of thetorchjoined to the nozzle, the internal diameter of said distributinginsert being larger than the diameter of the external wall of theinternal tube, while the external diameter of the distribution insert issmaller than the diameter of the internal wall of the external mantle, agap for the passage of the cooling liquid being provided between thefront face of the nozzle and the front face of the distribution insert,the torch head housing a distribution chamber arranged axially slidablein the torch head and bearing a tubular holder of the carhode andanother tube of electrically insulating material, surrounding thistubular holder, the space between the tubular holder and theelectrically insulating tube serving for the supply of the stabilizinggas, the torch head consisting of a sleeve and a cover, mutuallyconnected by a nut, allowing the adjustment of their axial position, thedistribution chamber being urged by spring force against the bottom ofthe cover of the torchhead.

By a suitable selection of the mutual adjustment of the supply of thestabilizing gas and of the working end of the cathode, one plasma burnercan be used with very small and with large amounts of working gas whileusing nozzles of different diameter. By eliminating consequences ofchanges of the supply of the stabilizing gas with respect to the workingend of the cathode together with a mechanism for adjustment of thedistance of the cathode from the anode, forming afterstarting acomplementary unit controlled in the torch head, the whole design of thetorch and its operation is substantially simplified. By providinglongitudinal grooves on the cathode surface a perfect circumferentialdistribution of the axially streaming gas is achieved together with ahigher cooling effect of the cathode surface and if needed also with alaminary centric flow outlet of the plasma stream from the nozzle evenat higher outlet speeds. By using a directly cooled nozzle of the plasmatorch provided with a distribution insert with channels it is possibleto achieve with small cross sections for the passage high speeds of thecooling liquid along the working surface of the nozzle, reduce thethickness of the adhering layer of the streaming liquid and coolperfectly also the front part of the nozzle, the diameter of which canbe larger than the internal diameter of the distribution inlet.

DESCRIPTION OF DRAWINGS An examplory embodiment of a plasma torchaccording to this invention is shown in the attached drawings where FIG.1 is a longitudinal sectional schematic view of the whole torch,

FIG. 2 the arrangement of the cathode with longitudinal surface groovesand of the nozzle with the distribution inlet in elevation with parts inlongitudinal sectional view and FIG. 3 a cross section along a planeindicated in FIG. 2 by A-A showing the mutual arrangement of thecathode, the nozzle and the distribution inlet.

DESCRIPTION OF PREFERRED EMBODIMENT The plasma torch according to thisinvention has a nozzle 1 functioning as an anode and joined to twoconcentric metal tubes, forming the external mantle 21 of the wholetorch and an internal tube 22, furthermore a cathode 3 fixed on anelectrically conductive holder 6 of the cathode 3. The nozzle 1 of theplasma torch is made of copper or of some metal having a high meltingpoint and is intensively cooled by some liquid flowing along itsinternal surface as indicated by arrows. A sufficient speed of theflowing liquid at the internal surface of the nozzle 1 is secured by adistributing insert 23 fixed to a separating tube 2 arrangedconcentrically between the external mantle 21 and the internal tube 22of the torch. It is to be noted that the separating tube 2 is secured inthe sleeve and simultaneously constitutes a reinforcing part of thedistributing insert 23. The separating tube 2 is constructionallydifferent from the external mantle 21. The separating tube 2 is fixed tothe sleeve 9. The supply and removal of the cooling liquid to and fromthe nozzle is achieved by the inlet 7 and by the outlet 8 respectivelyof the cooling liquid. The cathode 3 which is affixed to the holder 6 ismade of a high melting metal, is hollow and is cooled by liquid which issupplied to its working end via an inlet tube 4, and is removed over theoutlet20 of cooling liquid of the cathode 3. As stated above, the nozzle1 functions as an anode, during the starting period the positive pole ofan auxiliary DC. current source being connected to the nozzle. Duringsuch starting period an independent arc burns between the anode, that isthe nozzle 1, and the cathode 3. The independent arc enables thecreation or ignition of an independent arc buring between the cathodeand the material to be smelted. The dependent arc, stabilized by thegas, then burns through the nozzle 1. The stabilizing gas is supplied toa distribution chamber 16 via a gas inlet 17, wherefrom it passes to thedischarge chamber of the torch along a tube of electrically insulatingmaterial fixed to the distribution chamber 16. The space defined betweenthe holder 6 of the cathode 3 and the tube 5 forms an axial gas supply.The torch head proper consists of the sleeve 9, of a nut 12 and aclosure 15 and houses a device for adjustment of the supply of thestabilizing gas and a mechanism for starting and for adjustment of thedistance of the cathode 3 from the nozzle 1. This adjustment of thedistance of the cathode 3 from the nozzle is accomplished by turning thenut 12 provided on both ends with right and left hand threads. Whenturning the nut 12, the distance between the closure 15 and the sleeve 9is changing, whereby simultaneously the distribution chamber 16 isaxially displaced, its constant contact with the bottom of the closurebeing secured by the pressure of the spring 14 acting on thedistribution chamber 16 by way of a washer 13 of electrically insulatingmaterial. Simultaneously with the distribution chamber 16 the porcelainetube 5 connected therewith is displaced, along which'stabilizing gas issupplied to the nozzle of the torch and equally also the holder 6 withthe cathode 3. The movement of the distribution chamber 16 istransmitted to the holder 6 of the cathode 3 by three set screws 18.

The lower end of the tube or holder 6 which forms the cathode 3 is ofsmaller diameter than the holder 6, the cathode being joined to theholder 6 by a frustoconical portion, as shown. The anode is formed as alower end of the tube 22, such lower end being of smaller diameter thanthe upper, main portion of such tube. The lower and upper portions oftube 22 are joined by a frusto-conical portion which is coaxial of thefrusto-conical portion of the cathode. the two frusto-conical portionshaving substantially the same apex angle. As will be seen in FIG. 1, theupper, largerdiametered end of the frusto-conical portion of cathode 3has substantially the same diameter as the lower, smaller-diametered endof the frusto-conical portion of the nozzle 1. It can be seen from theabove that the adjustment of the effective distance between the cathode3 and the anode 1, that is the length of the gap between thefrusto-conical portions thereof, is performed by adjusting the nut 12.The adjustment of the distance between the working end of the cathode 3and the mouth of the stabilizing gas supply is carried out afterloosening the screws 18in such way that the cathode is retracted into orextended out of the tube 5 which constitutes the supply of thestabilizing gas.

FIG. 2 shows the arrangement of the cathode with longitudinal grooves onits surface and of the nozzle provided with the distributing insert. Thecathode 3 has longitudinal grooves 26 for the passage of the gas C andis by means of the tube 5 from electrically insulating materialcentrically guided in the nozzle 1. The nozzle ll of the plasma torchhas a front face with a rim, provided on its circumference with apacking ring 27 of rubber. The distribution insert 23 engages with itsextremity into the cavity formed by this rim, determining the coaxialposition of the distribution insert 23 with the whole torch. Channels 24are provided on the external circumference of the distribution insert 23enabling access of the cooling liquid B to the working surface of thenozzle 1. Due to this accurate guiding of the distribution insert 23with respect to the nozzle 1, it is possible to provide a very smallcross section for passage of the cooling liquid B between the cooledwall of the nozzle 1 and the internal wall of the distribution insert23. The track along which the cooling liquid B is flowing is indicatedin FIG. 2 by arrows. The space for the supply of the cooling liquid B tothe nozzle is determined by the internal surface of the external mantle21 and the external surface of the distribution insert 23. FIG. 3 showsone possible arrangement of the channels 214 in the distribution inserts23 in cross section including a part of the torch.

The nut 12 and the closure 15 are made of electrically insulatingmaterial. The porcelaine tube 5 is sealed by a packing ring 10. Anoptimum adjustment of the gas supply and of the working end of thecathode 3 can be accomplished after loosening the set screws 18. Thesealing of the holder 6 of the cathode 3 is accomplished by a packingring 19. The starting of the torch is performed either by the use of anionizer or by pressing the holder 6 of the cathode 3 in directiontowards the nozzle 1 against the force of the spring 14 resting againstthe washer 11 made of electrically insulating material. The cathode 3 isthrust downwardly (FIG. 1) until the upper, larger-diametered end of itsfrusto-conical portion engages the lower, smallerdiametered end of thefrusto-conical portion of the anode l to create a short circuit betweenthe cathode and the anode, and to start an electrical discharge therebetween when the cathode is separated from the anode; and aftersubsequent release of the force acting on the holder 6 of the cathode 3the cathode 3 returns spontaneously into its original position due tothe force of the spring and if the plasma torch is connected to a sourceof electrical current, an electric are between the cathode 3 and thenozzle 1 is started. The connection of the plasma torch to the source ofelectric current is made by terminals on the external mantle 21 and onthe holder 6 of the cathode 3. The possibilities of application and therange of output of the plasma torch can be changed by changing the sizeof the nozzle 1, of the cathode 3 and of the distribution insert 23.

The described plasma torch is suitable for cutting of ferrous and nonferrous metals and alloys, for welding of steel, of non ferrous alloysand of metals with high melting point such as molybdenum, tungsten andsimilar. This arrangement of the plasma torch is particularly suitablefor band raffination and for melting of metallic material having amedium or high melting point. After adjustment of the nozzle the torchis also suitable for spray coating with layers of metal or of oxides.

! claim:

1. Plasma torch with axial supply of a stabilizing gas comprising incombination:

a torch head comprising a sleeve, a cover and a nut connecting both thesleeve and cover, the nut enabling an adjustment of the axial distancebetween the cover and the sleeve,

a nozzle forming the anode of the torch, connected by an internal tubeand an external coaxial mantle with the sleeve,

a coaxial separating tube fixed to the sleeve, dividing the spacebetween the internal tube and the external mantle into two coaxialannular spaces, communicating near the front face of the nozzle, meansfor supply and removal of a cooling liquid to and from said annularspaces,

the separating tube extending into a distributing insert, leaving anarrow space at places adjacent to the operating surfaces of the nozzle,

means for securing the position of the distributing insert with respectto the nozzle while leaving free passages for the cooling liquid,

a distribution chamber arranged axially slidable within the torch head,

a tubular holder fixed to this distribution chamber and extending intothe space of the internal tube,

a cathode fixed to the extremity of this holder,

an inlet tube for a cooling liquid for the cathode inserted into thisholder dividing its space into two annular spaces communicating near thehead of the cathode,

means for supply and removal of the cooling liquid to and from theseannular spaces,

a tube of electrically insulating material fixed to said distributingchamber and engaging into the space between the internal tube and theholder of the cathode,

means for supplying a stabilizing gas into the space between the holderof the cathode and the tube of electrically insulating material,

the external surface of the cathode provided with longitudinal grooveslimiting the passage of the stabilizing gas through the nozzle,

spring means urging the distributing chamber against the bottom of thecover of the torch head.

2. Plasma torch as in claim 1, the tubular holder of the cathode beingconnected with the distribution chamber by means, allowing theadjustment of their relative axial position.

1. Plasma torch with axial supply of a stabilizing gas comprising incombination: a torch head comprising a sleeve, a cover and a nutconnecting both the sleeve and cover, the nut enabling an adjustment ofthe axial distance between the cover and the sleeve, a nozzle formingthe anode of the torch, connected by an internal tube and an externalcoaxial mantle with the sleeve, a coaxial separating tube fixed to thesleeve, dividing the space between the internal tube and the externalmantle into two coaxial annular spaces, communicating near the frontface of the nozzle, means for supply and removal of a cooling liquid toand from said annular spaces, the separating tube extending into adistributing insert, leaving a narrow space at places adjacent to theoperating surfaces of the nozzle, means for securing the position of thedistributing insert with respect to the nozzle while leaving freepassages for the cooling liquid, a distribution chamber arranged axiallyslidable within the torch head, a tubular holder fixed to thisdistribution chamber and extending into the space of the internal tube,a cathode fixed to the extremity of this holder, an inlet tube for acooling liquid for the cathode inserted into this holder dividing itsspace into two annular spaces communicating near the head of thecathode, means for supply and removal of the cooling liquid to and fromthese annular spaces, a tube of electrically insulating material fixedto said distributing chamber and engaging into the space between theinternal tube and the holder of the cathode, means for supplying astabilizing gas into the space between the holder of the cathode and thetube of electrically insulating material, the external surface of thecathode provided with longitudinal grooves limiting the passage of thestabilizing gas through the nozzle, spring means urging the distributingchamber against the bottom of the cover of the torch head.
 2. Plasmatorch as in claim 1, the tubular holder of the cathode being connectedwith the distribution chamber by means, allowing the adjustment of theirrelative axial position.